Photovoltaic (PV) elements, such as e.g. solar panels, are known to convert solar energy into direct current (DC). The solar energy can be fed into the electrical AC grid by means of a string inverter, wherein series connected panel are directly connected to the input of the string inverter. A DC/DC boost converter is used in the input stage of the string inverter to adapt the voltage to a desired level to the next DC/AC converter stage. The DC/AC converter stage converts the intermediate voltage into an alternating current (AC) which can be fed into existing electrical grids. Since the output power of a PV panel is determined by a non-linear relationship between voltage and current, a partial shadowing of a PV panel may cause a great reduction in its output and greatly increase its internal resistance. As the panels are connected in series, a power mismatch between PV panels may lead to a drastic and disproportionate loss of power from the entire solar array. Events like a passing shadow, or differences in panel performance due to pollution, differential aging, or differences during manufacturing, may hinder the array as a whole to operate at its peak efficiency point.
One attempt to address this issue is to connect a micro-inverter to each PV panel. Each micro-inverter tunes the output of their respective PV panel and directly outputs an AC that can be feed to the existing electrical grid. By connecting the micro-inverter outputs in parallel, the array of PV panels may be less sensitive to shadowing or failure of single PV panels. One drawback of this approach is however the relatively high cost of the micro-inverters. Another disadvantage is the large voltage conversion ratio which results in a relatively low efficiency.
A different attempt to address the same issue is to add DC/DC converters, so called power optimizers, to each PV panel. The outputs of these DC/DC converters are series connected and fed to a string inverter. This also allows tuning the output of the respective PV panels. The drawbacks are similar to the drawbacks of the micro-inverters, i.e. reduced efficiency and increased cost.
Thus, there is a need for providing an alternative method of feeding solar energy into the grid such that the overall conversion efficiency and performance, also at partial shading and mismatched panel powers, is improved.